SAN DIEGO (CNS) - San Diego's tight housing market squeezed renters this spring as the county's apartment vacancy rate plunged to 3.7 percent, down from 5.4 percent last fall, the San Diego County Apartment Association reported Monday.

In the city of San Diego, the vacancy rate was 3.3 percent. The East County and South Bay had the lowest vacancy rates at 3.7 percent, while the North County's was at 5.1 percent.

The SDCAA said units with three or more bedrooms had the highest vacancy rate at 5.7 percent.

Studios offered the lowest vacancy rate at 2.8 percent, while two- bedroom units experienced a drop from 6 percent last fall to 3.5 percent in the spring. The vacancy rate for one-bedroom units was 3.7 percent.

"The rise in vacancy rates for units with three or more bedrooms could be indicative of an uptick in single people or couples without children searching for smaller-sized units," said SDCAA Executive Director Alan Pentico. "While the decrease in vacancy rates for studios reinforces the fact that despite all the multifamily construction, San Diego remains in a housing deficit."

The association conducts surveys on vacancy rates and rents each spring and fall.

In the spring survey, the average rent was $1,158 for studio units; $1,432 for one-bedroom units; $1,763 for two-bedroom units; and $2,330 for units with three or more bedrooms.

Last fall, the average rents were $1,128 for studios; $1,531 for one- bedroom units; $1,789 for two-bedroom units; and $2,323 for those with three or more bedrooms.

"In San Diego, we've seen the jobless rate steadily decline, giving people the financial means to seek out a non-roommate living situation and offering another possible explanation to the rise in rents for studio units," Pentico said.

Prospective buyers have also had to deal with a tough market, with low inventories of houses and condominiums for sale around San Diego County over the last year or so pushing median sales prices into record territory.